Regulating system



March 24, 1953 s o Tz 2,632,862

REGULATING SYS'TEM Filed May 2, 1950 WITNESSES: INVENTOR 5 4 1% Glenn E.Stolfz.

Patented Mar. 24, 1953 REGULATIN G SYSTEM Glenn E. Stoltz, Pittsburgh, Pa, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Application May 2, 1950, Serial No. 159,520

4 Claims.

This invention relates to regulating systems and, in particular, to are furnace regulator sys tems.

Arc furnaces and their operation are well known in the art. In general, there are three periods of melting down and refining of the metallic composition, usually rough scrap metal in the arc furnace, the first period being that necessary for melting the composition to the degree where the composition can be considered as being one body even though it is not completely melted. The next period is that covered by the complete melting of the composition, whereas the third period is the actual refining oi the molten composition, such refining requiring only sufiicient power for taking care of radiation losses and holding the bath at a given temperature.

During the first two of these periods, the furnace load may fluctuate to cause high surges on the power supply system unless care is exercised to control the current load. This may be appreciated when it is considered that pieces of the scrap metal composition may fall against the electrode, thus causing a direct short circuit or the pieces may fall away from the electrode to thereby reduce the load to a small value or to even extinguish the arc.

The usual regulating systems attempt to correct for such fluctuations in load by controlling the position of the electrodes to maintain a desired arc current and are potential. However, the adjustment of the position of the electrode is comparatively slow, with the result that the sudden changes incurrent drawn from the power circuit is not prevented, and objectionable variations in line voltage are encountered. The latter is particularlyobjectionable where the electric arc furnace is supplied from a power source which is being used to supply other apparatus, such as lighting equipment.

An object of this invention is to provide in an electric arc regulating system for efiecting a quick response to a change in load to limit the current flow to the load.

Another object of this invention is to provide in an arc furnace regulator system for an initial quick response to limit the current flow upon a change in load conditions while simultaneously therewith initiating a change in the positioning of the electrodes.

Other objects of this invention will become apparent from the following description when taken in conjunction With the accompanying drawing, the single figure of which is a diagrammatic view of an arc furnace regulating system embodying the teachings of this invention.

Referring to the drawing, an electric furnace I0 is illustrated, the furnace comprising a grounded receptacle 5? containing a bath of metallic material i l and three movable electrodes l6, I8 and 29. The electrodes l6, l8 and 2c are connected by conductors 22, 24 and 26, respectively, to the secondary winding 28 of a polyphase transformer 38, the primary winding 32 of which is connected by conductors 34, 35 and 38, respectively, to reactors d9, 42 and 44, respectively, the other end of the reactors being connected by conductors 4B and Eli, respectively, to the three-phase supply circuit comprising conductors 52, 54 and respectively.

Each of the movable electrodes is provided with a reversible motor for raising and lowering it and a regulating system for limiting the current flow to the electrode and for governing the operation of the motor in accordance with changes in the current flowing through the electrode and the potential across the electrode arc. Since the regulating system associated with each electrode and motor is of like construction and operates in the same manner, only one of the regulating systems and motors for limiting the current flow and controlling the positioning of the electrodes is illustrated.

In the drawing, a reversible motor 58 comprising an armature winding 68 and two opposed series field windings t2 and 64 is illustrated 'for raising and lowering the electrode 16. As illustrated, one end of the armature winding 60 is connected to the negative terminal of a source of power, the other end of the armature 60 being connected to one end of each of the opposed series field windings 62 and 6:1. The other ends of the field windings E2 and i i are connected by conductors (it and E58, respectively, to the spaced stationary contact members and 12, respectively, and are disposed to be connected to the positive terminal of the source of supply by the movable contact member M which is actuated by the relay it, as will be explained more fully hereinafter. The armature 60 of the motor 58 is mechanically connected to the electrode 16 in any suitable manner for eiiecting movement thereof and in the embodiment illustrated is connected by the shaft 13, a winding drum Bil and a flexible conductor 32 which passes over pulleys 8d and '86.

As illustrated, in order to control the current supplied to the electrodes, a pair of make-alive valves 83 and are disposed and so connected apart as to shunt a part or all of the reactor 46 when the valves are alternately conducting. A similar pair of valves is connected in circuit acsaeca relation with each of the reactors i2 and MI connected in the other phases of the input circuit. The valves 88 and 96 are of standard construction having an anode 92, a cathode M, and a make-alive electrode or immersion igniter control member 96 normally in permanent contact with the cathode t l. In the circuit illustrated, the make-alive valves 38 and 98 are connected to the supply circuit 52, ed and a transformer 68 being connected thereto for supplying a control potential to the pair of valves 86 and Q6. The transformer 63 is provided with a plurality of secondary windings I66, I62 and IM which are so connected as to supply the control potential to the pair of valves associated with the reactors 86, 62 and 2 respectively. The control potential circuit for supplying the valves 38 and 66 is formed or a constant potential network we and a wave-shape transforming circuit I68 disposed between the secondary winding I66 of transformer 96 and a transformer Ilil, the secondary windings H2 and Ilil of which are connected across the make-alive electrode 96 and the cathode es of the valves 68 and 6t, respectively.

The constant potential network W6 comprises a suitable three legged reactor I I6 preferably of the non-linear or saturable variety in series with the supply of control potential, a second saturable reactor I I6 in shunt with the control potential and a capacitor I26 in shunt with the saturable reactor H6. By suitably varying the reactance of the non-linear reactor M6, the phase angle of the control potential may be shifted.

The reactance of the reactor H6 is controlled by applying a variable direct-current biasing potential on the direct-current winding I22 carried on the center leg of the reactor IIE from a battery I24 by adjusting a rheostat I26 which is connected in series therewith.

The rheostat I26 is controlled by a balanced beam type of regulator I26 in response to changes in the current flowing in the electrodes I6 and of the potential across the arc. As illustrated, the balanced beam regulator I28 is provided with a movable arm I36, the end of Which is in electrical engagement with rheostat I26 and which is connected to one end of the rheostat for effectively shunting or connecting the rheostat in circuit as the arm I36 is actuated. The arm I3!) is carried on the beam I32 which is pivotally supported as at I34, control electromagnets I36 and I38 being disposed at each end of the beam I32 responsive to current and to voltage changes, respectively. The winding of the electromagnet I36 is connected by the current transformer I26 to be responsive to the current flowing through the electrode It, whereas the winding of the electromagnet I38 is connected across the conductor 22 and the receptacle I2 to be responsive to the are potential.

The constant potential network draws a larger load current than the firing circuit for the valves 88 and 96 alone but, in turn, acts as a source of power for the firing circuit. The parallel combination of the capacitor I26 and the reactor H6 is preferably designed so that at 100% supply voltage the combination will draw the minimum of current. If the supply voltage should for any reason be lowered, then the capacitor I26 draws a charging current in excess of the magnetizing current of reactor I it which, in conjunction with the load current, causes a leading current to be drawn through the phaseshifting reactor II6, thus causing a drop for maintaining substantially full-voltage supply to the wave distorter circuit I 66. On the other hand, if the supply voltage is high, then the saturating reactor IIB draws a magnetizing current in excess of the charging current drawn by the capacitor I26 which, in conjunction with the load current, causes a lagging current to be drawn through the phase-shifting reactor H6, thus causing a drop which maintains the voltage at the wave-distorter circuit substantially constant. The constant potential network I66 thus makes it possible to obtain as great as a phase shift with no appreciable change in peak voltage output while at the same time maintaining substantial constant voltage at the wave distorter circuit even though the supply voltage changes as much as 30%.

The wave-shape transforming or distortin circuit I68 comprises a capacitor I42 connected in shunt with the constant potential network with an impedance such as a resistor or the linear reactor IM connected therebetween for controlling current flow to the capacitor I42. The opposite sides of the capacitor I42 are connected to the outer terminals of transformer I II), a non-linear inductance such as the saturating reactor Hi6 being connected between the common terminal of reactor I44 and capacitor I42 and the transformer. The saturating reactor produces sharply peaked impulses of alternating polarity which are supplied to the transformer.

In order to control the potential of the primary windings of the transformer I I6, suitable rectifier elements and unidirectional conducting devices I48 are connected between the wave-distorter circuit and the primary winding of the transformer, whereas rectifier elements I50 are connected across the wave-distorter circuit and to the common tap of the primary windings of the transformer III). In addition, rectifier elements are disposed in circuit with the secondary windings H2 and H4 and the associated make-alive electrodes 96 for controlling the direction of current flow thereto. By this means, the primary windings of the transformer IIB are alternately energized and by-passed and the valves 86 and 30 are alternately fired to control the current flowing to the primary winding 32 of the transformer 36.

In operation, assuming that the system is energized and in the position shown with the electrodes I6, I6 and 2:) in position for maintaining an arc with the metallic composition Hi, the system is in substantial balance, the current flowing through the electrode and the potential across the are being of some predetermined value. If for any reason the system becomes unbalanced such as where a part of the metal of the bath I4 falls in on the electrode I6, a direct short circuit is encountered with the result that the current flowing through the electrode is greatly increased. Immediately upon the increase in the current flowing through the electrode I6, the winding of the electromagnet I36 of the balanced beam regulator I23 is so energized and the winding of the potential electromagnet is so deenergized that the beam I32 pivots in a clockwise direction about its pivot I34 to connect additional sections of the rheostat I26 in circuit with the battery I24 and the directcurrent winding I22 of reactor H6.

The connecting of additional sections of the rheostat I26 in circuit with the direct-current winding I22 immediately efiects a decrease in the direct current flowing through the winding I22 and thereby effects an increase in the reactance of the reactor H6 to so shift the phase of the control potential supplied from the secondary winding H30 as to retard the firing time of the pair of valves 88 and 90 and thereby decrease the current passed by the valves 88 and 90 to immediately limit the current supplied to the furnace.

At the same time that the phase angle of the control voltage is changed to effect an immediate change in the current supplied to the furnace, the change in the reactance of reactor H 5 effects a decrease in the voltage across the conductors to which the parallel connected capacitor 529 and reactor H8 are connected. This decrease in the voltage effects a decrease in the energization of the winding of relay 7% whereby the movable contact member 74 is actuated into engagement with the stationary contact member 12 to close the circuit extending from the positive terminal of the source of supply through the contact members It and I2, conductors 68, field winding 64 and the armature winding 66 to the negative terminal of the source of supply to effect an operation of the motor 58 whereby the electrode H5 is raised to eifectively decrease the current flowing through the electrode and increase the arc potential.

If, on the other hand, the change in the current flowing through the electrode [5 is a decrease, as by reason of the metallic composition 14 falling away from the electrode it, then the electromagnet i38 is so energized and the electromagnet ififi is so deenergized as to effect a counterclockwise movement of the beam I32 about its pivot i3 2 to effectively shunt more of the rheostat I28 from the circuit with the battery I24 and the direct-current winding in to thereby increase the direct-current flowing in the winding I22 and decrease the reactance in the constant potential circuit. This decrease in the reactance of reactor 4 it so changes the phase angle of the control voltage as to effect an advance in the ring time of the valves 8-8 and 9!} whereby the valves 88 and 96 pass more current to immediately increase the current supplied to the arc furnace.

At the same time, the change in the reactance of reactor I 16 in the constant potential circuit effects an increase in the voltage across the conductors to which the winding of the relay E6 is connected whereby the relay i5 is so energized as to actuate the movable contact member 74 into engagement with the stationary contact member It to close a circuit which may be traced from the positive terminal of the source of supply through contact members M and H3, conductor E6, field winding 62 and the armature winding SE! to the negative terminal of the source of supply to cause the motor 58 to operate in such a direction as to lower the electrode [6, and thereby increase the current flowing through the electrode and decrease the are potential.

In the system of this invention, it will be appreciated that if the current flow through the electrode i6 is excessive and of sufficient magnitude that the reactance of reactor Hi3 will be so changed as to render the valves 88 and 953 inoperative, the reactor .9 will be connected to the supply circuit and will immediately limit the current flow to a safe and satisfactory value even though the furnace electrode I6 is short circuited. By connecting the valves 58 and 99 in the manner described in circuit with a portion of the reactor 48, the amount of current flowing under condition of minimum arc voltage drop can be adjusted.

The system described is very sensitive to changes in current and voltage effecting an immediate operation to control the current supplied thereto while at the same time providing for initiating a physical movement of the electrode it to position the electrode and thereby provide a positive control of the arc current and are potential. The advantage of the quick response regulating feature in conjunction with the slower responsive motor operation can be readily appreciated for if the short circuit is of only momentary duration, the necessary protection against excessive current is obtained and where the short circuit is only of momentary duration, the protection thus obtained is sufficient without effecting a physical movement of the electrode l6, since the time delay in the actuation of the motor 58 may be so large that the surge is over before the motor is energized for operation.

I claim as my invention:

1. In an arc-furnace regulator system, in combination, a source of alternating-current power supply, a movable electrode connected to the power supply for drawing an arc, a motor disposed for raising and lowering the electrode, a pair of make-alive valves connected in circuit between the power supply and the electrode, the make-alive valves being disposed for firing to alternately pass current from the power supply to the electrode, a source of control potential for the valves, a phase-shifting circuit including a variable reactor connected in series with the output of the source of control potential, a reactor and a capacitor connected across the source of control potential and the variable reactor, circuit means disposed to be responsive to the current flow through the movable electrode and to be responsive to the voltage across the electrode arc to produce a signal that is a measure of the arc current and the arc voltage, the variable reactor being responsive to the magnitude of said signal to thus vary the reactance of the variable reactor to shift the phase angle of the control potential to control the firing of the tubes and thereby control the current flow through the movable electrode, and means also responsive to said signal for controlling the motor to position the movable electrode.

2. In an arc-furnace regulator system, in combination, a source of alternating-current power supply, a movable electrode connected to the powei supply, a motor disposed for raising and lowering the electrode, a pair of make-alive valves connected in circuit between the power supply and the electrode, the make-alive valves being disposed for firing to alternately pass current from the power supply to the electrode, a source of control potential for the valves, a phase-shifting circuit including a variable reactor connected in series with the output of the source of control potential, a reactor and a capacitor connected across the source of control potential and the variable reactor, means responsive to the arc current and the are potential for varying the reactance of the variable reactor to shift the phase relation of the control potential, a wave distorter circuit fed by the source of control potential through the phase-shiftin circuit, a make-alive electrode in each of the valves, means for selectively energizing the make-alive electrodes from the output of the wave distorter circuit to control the firing of the tubes and thereby control the current flow to the electrode, and means also responsive to the arc current and arc potential for controlling the motor to position the electrode.

3. In an arc-furnace regulator system, in combination, a source of alternating-current power supply, a movable electrode connected to the power supply, a motor disposed for raising and lowering the electrode, an impedance connected in circuit between the power supply and the electrode, a pair of make-alive valves disposed to alternately shunt at least a portion of the impedance, a source of control potential for the valves, a phase-shifting circuit including a variable reactor connected in series with the output of the source of control potential, a reactor and at capacitor connected across the source of control potential and the variable reactor, means responsive to the arc current and the arc potential for varying the reactance of the variable reactor to shift the phase relation of the control potential, a wave distorter circuit fed by the source of control potential through the phaseshifting circuit, a make-alive electrode in each of the valves, means for selectively energizing the make-alive electrodes from the output of the wave distorter circuit to control the firing of the tubes and thereby control the current flow to the electrode, and means also responsive to the arc current and are potential for controlling the motor to position the electrode.

4. In an arc furnace regulator system, in combination, a source of alternating current power supply, a movable electrode connected to the power supply, a motor disposed for raising and lowering the electrode, a pair of make-alive valves connected in circuit between the power supply and the electrode, the make-alive valves being disposed for firing to alternately pass current from the power supply to the electrode, a source of control potential for the valves, circuit means associated with the movable electrode to produce a signal that is a measure of the arc current and the arc potential, means responsive to the signal for shifting the phase relation of the control potential to control the firing of the tubes and thereby control the current fiow to the electrode, and means also responsive to the signal for controlling the motor to position the electrode.

GLENN E. STOLTZ.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,573,095 Saklatwalla et al, Feb. 1 6, 1926 1,969,550 Evans Aug. 7, 1934 2,242,948 Gulliksen May 20, 1941 2,248,020 Freudenhammer July 1, 1941 2,259,958 Levy Oct. 21, 1941 2,441,789 Bivens May 18, 1948 FOREIGN PATENTS Number Country Date 596,726 Great Britain Jan. 9, 1948 

